High voltage condenser



Sept. 14, 1948. B. B. MlNNlUM I I 2,449,303

I 'HIGH VOLTAGE CONDENSER Filed Nov. 2;), 1945 2 Sheets-Sheet 1 INVENTOR Ema/v a. M/N/v/qM BY Pwwa pmfiam :Zmwd

HI! ATTORNEYS Sept. 14, 1948. B. B. MINNIUM HIGH VOLTAGE CONDENSER 2 Shets-Sheet 2 Filed Nov. 23, 1945 INVENTOR BYRON 6. M/NN/UM #7; ATTORNEYS Patented Sept. 14, 1948 HIGH VOLTAGE CONDENSER Byron B. Minnium, Erie, Pa., asslgnor to Eric Reslstor Corporation, Erie, Pa., a corporation of Pennsylvania Application November 23, 1945, Serial No. 630,184

Claims. 1

This invention relates to variable condensers and more particularly to an improved rotatable variable condenser of the solid dielectric type adapted to withstand high potential differences between its plates.

In constructing condensers for use in high potential circuits, and particularly where such circuits are operated at high frequencies, it is important to eliminate phenomena such as the corona discharge which, especially at high frequencies, may undesirably affect the apparatus.

shown in Fig. 1 arranged in the form of a gang condenser, the section being taken on line 4-4 I of Fig. 5;

Fig. 5 is a transverse section taken on line I! of Fig. 4; and

Figs. 6 and 7 are fragmentary showing details.

Referring now to these drawings, and first to Figs. 1-3, inclusive, the condenser comprises a The prime object of the present invention, there- I material such, for example, as ceramic material,

have their contacting faces in intimate gliding contact with one another, these surfaces being ground to a degree of smoothness which will provide such contact. The condenser plates are in the form of metallic films on the outer, nonengaging surfaces of the rotor and stator. In order to provide the condenser plates with corona shields and also to bring the surfaces of the rotor and stator plates into close proximity these films are applied to sector-like depressions formed in the outer-suriaces-of the rotor and stator elements. Difiiculty has been experienced, however, in providing for the rotatable adjustment of the rotor while maintaining face-to-face contact with the stator; and another object of the invention is to eliminate this difficulty and at the same time avoid a construction favorable to the production of corona discharge.

Another object of the invention is to provide a high potential variable condenser of simple arrangement and having a unit construction which is well adapted for use in the gang type of condenser.

The invention will be understood from a consideration of the accompanying drawings illustrating two embodiments thereof by way of example. In these drawings:

Fig. 1 is a central vertical section of the improved variable condenser;

Fig. 1a is a section taken on line ia--la of Fig. 3 to show a detail;

Fig. 2 is a view in transverse section taken on the line 2-2 of Fig. 1;

Fig. 3 is a similar view taken on line 3-3 of Fig. 1 with parts broken away;

Fig. 4 is a view in horizontal longitudinal section of a modification of the condenser unit stator element l, preferably square in shape, and

a rotor element 2 which is preferably a round disk, both of these elements being made preferably of a ceramic material. Rotor 2 is rotatably adjustable with respect to the stator and is mounted with its inner face in contact with the inner face of the stator. These inner faces of both elements are ground to a smooth finish so that when the rotor is ad usted they move in intimate gliding contact.

Stator element 1 is secured to a frame structure comprising a front plate 3 of electrically insulat ing material such, for example, as a tough resinous plastic composition. Its character and thickness are such as to provide a rigid support for the stator l to which it is secured by means of four spacing studs, one at each corner, into the ends of which screws 6 are threaded. Plate 3 may be attached to an instrument panel *8 by any suitable means (not shown).

Rotor 2 is provided with an adjusting shaft l which is supported in apertures in plate it at the front and in a bracket 9 at the back. Bracket 8 is of insulating material preferably similar to that of plate 3 and. is mounted on the frame structure in any suitable manner, as, for example, by means of the lower two screws 5. Shaft 1 passes through a central aperture in stator l, and rotor 2 is mounted upon the shaft in a mannor to be described later on.

Stator i in its rear surface has a sector-like depression '9 bounded on its outer side by a substantially half-circular are W- (Fig. 2) and on the inside by a concentric are H leaving a hub portion l2 at the center of the stator. The ends of depression 9 are shown as bounded by two radial lines I! and it passing horizontally through the center of shaft 1 thereby making the depression substantially in angular extent in order to obtain the highestcondenser capacity.

In depth, depression 9 extend preferably more than half the thickness of stator element 5 so as to place the bottom of the depression as close to the inner face of the stator as is consistent with the required dielectric breakdown strength. Depressien 8 is substantially flat throughont its area sectional views 4 2l,-thaws except at the margins, all of its margins, however, being flared as shown in Fig. 1 and by the shading in Fig. 2.

The stator condenser plate I9 i formed by coating the surface of depression 9 in any desired manner with a metallic film, for example, of silver. This film extends throughout the flat area of the depression and also throughout the flared margins to both the inner and outer rims of the depression (formed by the arcs I9 and II) and also to the ends of the depression formed by radial lines I3 and I4. These flared portions constitute a corona shield.

Th connection terminal for stator condenser plate I5 is a metal strip l9 terminating in a contact spring at its inner end to engage the surface of the condenser plate. Strip I9 is mounted between cleats I1 and I8 fastened to stator I. These cleats are of an insulating material having a lower dielectric constant than the material of stator I.

A depression I9 somewhat similar to depression 9, may b provided in the opposite half of the rear surface of stator I. In the embodiment shown the surface of depression I9 is not coated with metal and it is somewhat smaller in area than depression -9, its straight edges I3a and Ila being parts of a chord parallel with the radial edges I3 and Il. As will appear later, however. depressions 9 and I9 may have equal areas, the straight edges I3 and ll of the depressions both being parts of chords instead of radial lines.

Rotor element 2 consists of a circular disk preferably of ceramic material having a depression 9a which is geometrically similar to and substantially co-extensive in area with depression 9 of stator I. Like depression 9, it is bounded by the outer and inner concentric arcs "la and Na and by straight edges I3a and Ila, leaving a hub portion I 2a at the center of the rotor. Rotor 2.is also preferably provided with a second and similar depression I9a having the same area as depression I9. The ends of depression I9a are separated from the ends I3a and Ila of depression In so as to leave strengthening rib between them. Ribs 20 are parallel to a diametrical line passing through the center of rotor 2.

The surface of depression 9a of rotor 2 is coated with a metallic film to form a condenser plate Illa which is geometrically similar to and substantially coextensive with condenser plate I9 of the stator and is provided throughout its margins with an outwardly curved portion forming a corona shield.

It will be understood that the depth of depression 9a, like that of depression 9, is such as to leave only a thin portion of ceramic material (its thickness being determined by the required dielectric breakdown strength) throughout the fiat bottom of the depression so as to bring rotor condenser plate I5a as close to the inner ground face of the rotor as practicable. This places the two condenser plates I! and We as close together as possible when the condenser is adjusted to maximum capacity.

It will be understood that the adjustment oi" the rotor 2 by turning shaft 7 by means of a knob 2| on its outer end from the position shown in Fig, 1 where the two condenser plates I9 and lid are in registry, to the position where they have been turned 180 from each other, changes the condenser capacity throughout its range from maximum to minimum.

operating condenser plates. One pair is smaller than the other. and the depressions of each pair have the same area and geometric configuration. Thus, depressions 9 of stator I and 9a of rotor 2 are of equal area and configuration and constitute one pair, while depressions I9 and I9a are of the same area and geometric configuration but are smaller than the first pair. It will also be understood that when it is desired to provide a ,condenser having a lower maximum and also a lower minimum capacity the smaller depressions I9 and I9a may be metal coated to form the condenser plates, leaving depressions 9 and 9a uncoated.

For the purpose of mounting rotor 2 units adjusting shaft 1 in such a way as to maintain the inner ground surfaces of the stator and rotor elements in intimate contact in all positions of angular adjustment of the rotor, and also in order to key the rotor to the shaft, either 01' two constructions may be employed. These are shown respectively in Figs. 1 to 3 inclusive, and Figs. 4 to 7 inclusive. They may be used interchangeably. In Figs. 1 to 3 a spider 22 of conducting material is provided. This comprises a metal hub 29 which is fixed to shaft 1, for example by means of a set screw 2l, and which has at least three, and, as shown in Figs. 1 to 3, four, flexible fingers 25 and 29, fingers 25 being'somewhat longer than fingers 29.

Fingers 29 and 29 may be stamped out of suitable flexible resilient material such, for example, as phosphor bronze, and formed with an integral central portion 21. Central portion 21 may have a central aperture which may be slipped over a reduced portion 29 on hub 23, the end of which may be riveted over slightly on the outer surface of central portion 21 to hold the parts together.

The outer ends of fingers 25 are received in two recesses or indentations 29 (Fig. 'la) in depression 9a of rotor 2. The metallic film or coating which forms the rotor condenser plate Ila extends throughout the surfaces of recesses 29. The corona shield portions of condenser plate Iia extend beyond recesses 29 and the ends of fingers 29 to protect them. Electrical contact is made between spider 22 and condenser plate I9a by the ends of fingers 25.

The other pair of fingers 29 of spider 22 bear against the surface of the uncoated depression I9a 'on the opposite side of ribs 20, and in order to produce a potential gradient between fingers 29 and the surface of this depression thereby again reducing the tendency to the production of corona, buttons or small blocks 30 of insulating material having a lower dielectric constant than the material of which the rotor 2 is made are placed beneath the ends of fingers 29.

The connection terminal for the rotor condenser plate I-9a is indicated at II and comprises a strip of conductive material of resilient nature which is placedadJacent the inner surface of front plate 3 and at its inner end has an aperture through which adjusting shaft 1 passes. The inner portion of terminal 3| adjacent shaft I is slightly dished as shown at 32 in order to constitute a spring to maintain itself in contact with a washer 39 which is interposed between it and the surface of central portion 21 from which fingers 29 and 29 project.

Hub 29 is preferably provided at its left hand or inner end with a reduced portion N which forms a hub to assist in assembling the spider 22 and rotor 2. As shown in Fig. 1, however, reduced portion ll makes a loose fit with the II and Il being biased by the thrust of washer II and the inner end of terminal," against the surface of rotor I. Accordingly, the .turning of shaft I to adjust the capacity of the condenser.

will effect the rotation of rotor I without disturbing its intimate gliding contact with stator i and without interrupting the electrical connection between terminal II and rotor condenser plate lla.

Referring to Fig. 4, there is here shown a gang condenser which ismade up of four units similar wtmse'snows in Fig. 1. These units each comprising a single pair of stator and rotor elements lend themselves to assembly back to back to form sections as indicated at A and B which can be multiplied to obtain the desired condenser capacity, and to provide the required number of I condenser sections for simultaneous tuning of more than one circuit. As sections A and B are alike a description of only one of them will be given. I

Referring to section A two spiders ll are threaded on adjusting shaft 1a and fixed thereon by means of pins as indicated in the dotted lines.

Between them are suitable washers and a comemon terminal 38 for the two rotor condenser plates of the section. Each of these spiders has two pairs of ilexibie resilient fingers Ila and Ila which. as shown in Fig; 4, are arranged back to back being bent in opposite directions. As few as three and more than four fingers can be used if. preferred;

lnl 'inltotmlsbe'uscdinterchang lblr." 11seconstruction of spiders Iland rotors II and Ila is somewhatdiflerent from those of Figs. 1 to 3.

All four of the fingers Ila and Ila are of the same length and each has adiacent its end a formation ll preferably consisting of a small aperture.

On the bottom rotors I1 and Ila, two projecting "bumps" or'lugs ll are formed (Figs. 5 and 6) These are rounded protuberances on the flat surfaces of the depres sions and they are each covered with the metallic coating or film which forms the rotor condenser plates llb. This metal film thus "extends continuously over the entire depressed area lc. including lugs ll, in order to prevent the formation of corona. Electrical contact with plates ilb is made by the engagement of formations ll on fingers Ila with lugs ll.

Two upstanding lugs ll, similar in form to lugs ll, are provided'in the unmetallized depres sion llc which is formed on each rotor 180' from depression Ic. Over these lugs (Fig. 7) are preferably placed insulating collars II, and the apertures ll of nngers Ila are fitted onto *the upper reduced ends of such collars. Collars II are preferably of a material having a dielectric constant which is less than that of the material .of

the rotors so as to produce a potential gradient between fingers Ila and the surfaces ofthe rotors.

The fingers Ila and "a engaging lugs ll and v ll support and drive the rotors I1 and Ila allow- These two spiders 3l support on shaft 1a the respective rotor element I1 and 31a which are substantially like rotor elementI, a difference however being pointed out further on. The inner faces of each of rotor elements I! and 31a are arranged to move in intimate gliding contact with the inner faces of two stator elements ll and Ila, being held in engagement therewith by fingers Ila and Ila.

Stator elements 38 and 38a are of square shape similar to the stator element i and are supported upon an elongated frame which also supports the stator elements of section B and which consists of four elongated rods 39 upon which are received spacing collars 40 which serve to space-apart the four stator elements. At the opposite ends of rods 3! there are spacers ll which preferably are of the same length as collars l0.

A front frame member 42 is secured to the ends condenser to a panel such as indicated at M to which the device is -to be attached. Shaft la is supported in bearings ll and lla carried respectively in front frame I and in a rear frame member 42a secured to rear spacers ll. It will be understood that adjusting shaft la is provided with a turning knob Ila and that also suitable limit stop mechanism is provided. This may be in the form of a pin ll projecting from one side of shaft Ia and arranged to engage two struck-up portions 46 and ll of frame".

Referring now to Figs. 5, 8 and 7, a modified form of mounting for the rotor elements on the ing their ground surfaces to turn in gliding contact with those of the stator elements.

The connection terminals for the front and rear stator condenser plates llc are not shown in Fig. 4 but are of the contact spring type as shown in Fig. 1. The connection for the condenser piates llc of the two adjacent stator elements, ll of section B and 38a of section A, "consists of two opposed contact springs ll and ll. The shanks of these two springs are clamped between the sections of a split insulating collar ll which in turn is clamped between the rims of the stator elements" and Ila. Insulating collar ll is made of a'materiai having a dielectric constant which is lower than that of the stator elements.

As in the form of the invention shown in Figs. 1 to 3 inclusive, the stator elements ll and "a have two depressed areas so and llb, and both the rotor depressions 9c and llc and the stator depressions lb and Ill) are preferably of unequal area. In Fig. 4 the metallic coatings forming the several condenser plates have been shown as applied to the larger depressed areas 9!) and 8c with the smaller depressed areas ilb and ilc left uncoated. If desired, however, the reverse arrangement may beused, the smaller areas being coated to form condenser plates and the larger areas left uncoated. 'I'hen, if itis desired that certain of the sections of the condenser shown in Fig. 4 have lower maximum and lower minimum capacities, this may be accomplished by such reversal.

For example, should it be desired that section B have a lower maximum and lower minimum capacity than section A, the metallic coatings are applied to the smaller depressed areas llb and surfaces of depressions lc of" verse position. that is to say, with the smaller depressions lib and "c on the left instead of on the right.

In both forms of the invention described, the thickness of the' ceramic material of both the rotor and stator elements between the bottoms of the several depressions and the inner ground and lapped surfaces have been exaggerated for the sake of clearnes's of illustration. It will be understood, however, that such thickness of both the rotor and stator elements depends wholly on the working voltage of the condenser and the dielectric strength of the material of which the rotor and stator elements are made.

In other words, the material needs to be only of sufiicient thickness to prevent puncture of the dielectric by the voltage to be applied between the condenser plates. However, the height of the corona shields is determined not only by the working voltage but by the atmospheric pressure under which the unit is to operate. For example, the corona shields must be higher, that is to say, the depressed areas must be deeper, when the condenser is to operate at high altitudes than when it is to operate only at sea level.

By means of the present invention there is provided a high potential adjustable variable condenser which is extremely smooth in operation and which eliminates the possibility of the production of corona or similar effects. Itwill be understood that changes may be made in the construction shown in the two embodiments of the invention illustrated without departing from the spirit of the invention and that the scope thereof is set forth in the appended claims.

I claim:

1. In a variable condenser adapted to withstand high potential diiferences comprising stator and rotor elements of'dielectric material having inner faces in contact with one another, a rotor element having sector-like depressions in its outer face, a condenser plate applied to the surface of one of said depressions, an adjusting shaft for the rotor, and a spider of conducting material fixed thereto having at least three resilient fingers engaging said rotor, said fingers constituting the sole means of supporting said rotor in contact with said stator.

2. In a variable condenser adapted to withstand high potential diiferences comprising stator and rotor elements of dielectric material having,inner faces in contact with one another, a rotor element having sector-like depressions in its outer face, at least three lugs projecting from the bottoms of said depressions, a condenser plate applied to the surface of one of said depressions, an adjusting shaft for the rotor, and a spider 'of conducting material fixed thereto having resilient fingers with formations at their ends in engagement with said lugs, said fingers constituting the sole means of supporting said rotor'in contact with said stator.

3. In a variablev condenser adapted to withstand high potential differences comprising stator and rotor elements of dielectric material having inner faces in: contact with one another, a rotor element having sector-like depressions in its outer face, a condenser plate applied as a metallic coating to the surface of one of said depressions, at least three lugs-projecting from of supporting said rotor in contact with said stator.

4. In a variable condenser adapted to withstand high potential differences comprising stator and rotor elements of dielectric material having inner faces in contact with one another, a rotor element having sector-like depressions in its outer face, a recess in one ofsaid depressions disposed wholly within the periphery of the flared margin thereof, a condenser plate applied to the surface of said depression and said recess, an adjusting shaft for the rotor, and a spider of conducting material fixed thereto having at least three resilient fingers, one of which, is in engagement with said recess and the remainderof said fing s n ag ng said rotor through blocks'of material of a lower dielectric ,constantthan said rotor, said fingers constituting the sole means of supporting said rotor in contact with said sta 5. In a variable condenser adapted 'to withstand high potential difierences, a stator element, and a rotor element in contact therewith comprising a disk of dielectric material having two sector-like depressions in one face thereof, said depressions having fiat bottom surfaces with fiared margins, a condenser plate applied as a metallic coating to the surface of one of said depressions including the fiared margins thereof thereby forming a corona shield, an adjusting shaft for the rotor arranged to rotate substantially at right angles thereto and a spider of cmducting material fixed to said shaft, said spider having at least three resilient radially projecting fingers, one of said fingers being biased into engagement with said rotor condenser plate within the periphery of said corona shield, and the remaining fingers being biased into engagement with said uncoated depression within the flared margin thereof, said fingers constituting the sole means of supporting said rotor in contact with said stator.

BYRON B. MINNIUIL REFERENCES CITED The following references are of record in the file of this patent:

UNITED s'rs'ras harms Number Name Date 1,588,871 Gerber June 15, 1828 2,098,597 Saar Nov. 9, 1937 2,251,995 Godsey Aug. 12, 1841 2,326,341 Ehlers Aug. 10, 1048 FOREIGN PATENTS Number Country Date 525,018 Great Britain A118. 20. 1940 

